Semiconductor and other substrate-based wafers are typically fabricated or processed within multi-process “cluster tool” systems. A cluster tool is a manufacturing system that includes a set of environmentally isolated process chambers or modules, which are linked by a wafer-handling interface robot and a computer communications interface. The wafer-handling robot transports each wafer between the various modules in the system. The computer communication interface controls the sequential steps. There are several types of cluster tool systems, such as vacuum cluster tools for deposition and etching, lithography tools, chemical-mechanical polishing systems, ion implant tools and wafer inspection tools.
The wafer-handling robot has one or more articulated arms that support a wafer blade for carrying each wafer within the system. For example, a typical wafer-handling robot includes a pair of frog-leg type robotic arms that provide radial and rotational movement of the wafer blade in a fixed plane within the system. This movement is coordinated by the computer communications interface to pick up and drop off wafers and to transport the wafers between the various processing modules.
The wafer blade typically includes a relatively thin and planar piece of rigid material that supports the back surface of the wafer during transport. The wafer blade can also include an upwardly extending bridge at its distal end to assist in stabilizing the wafer.
Occasionally, slight alignment drift or shift of the wafer-handling robot or its arms can cause the wafer blade to contact the housing, the frame or another component in the system. This contact can release particles that can fall onto the wafer and cause defects. Since this type of contact is intermittent in nature, the contact can be nearly impossible to reproduce and can go undetected for a very long period of time. The intermittent nature of the contact often makes trouble shooting ineffective.
Currently, the only way to determine that there might be an alignment problem is to detect poor yields and high defect counts during a subsequent inspection step. In addition, the next inspection step may not occur until after several additional processing steps. This further adds to the difficulty in detecting and troubleshooting alignment problems. Therefore, the existing approach may not detect a problem until the damage is already done, or it may not detect the problem at all.
Improved methods and apparatus are desired for detecting or troubleshooting alignment errors in wafer-handling robots.